Publisher Summary This chapter discusses the scope of Ziegler catalysis; stereoselectivity, kinetics, and mechanism of Ziegler catalysis; homogeneous Ziegler–Natta catalysts; and side reactions in homogeneous catalysts. Ziegler catalysis involves rapid polymerization of ethylene and α-ole-fins with the aid of catalysts based on transition-element compounds, normally formed by the reaction of a transition-element halide or alkoxide or alkyl or aryl derivative with a main-group element alkyl or alkyl halide. There are thousands of patents involving every combination of pure or mixed main-group alkyls with transition-element compounds, each claiming advantages. The result of the early work led to the development of “second-generation” Ziegler catalysts. Polymers produced with unmodified Ziegler catalysts showed extremely high molecular weight and broad distribution, and in some cases, there was evidence for “living polymer.” All homogeneous catalyst systems for ethylene polymerization become heterogeneous when polyethylene is formed. On using vanadium-based homogeneous catalysts, polymers consisting of syndiotactic stereo blocks and stereo-irregular blocks are obtained. Very high stereoselectivity is observed for racemic 4-methyl- 1-hexene and racemic 3,7-dimethyl-1-octene, where the asymmetric carbon atom is in the α-position relative to the double bond. Stereoselectivity is caused by the chirality of the catalytically active center, and not by chiral atoms in the growing chain. It must be concluded from the results that reactions take place, which change the number of active sites present, due to the different behavior of the polymers in solution. Study of these new catalysts is intensive. After a short induction period, the activity of polymerization increases as a function of the monomer concentration.

Ziegler-Natta Catalysis

Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities Christophe Copeŕet,*,† Aleix Comas-Vives,† Matthew P. Conley,† Deven P. Estes,† Alexey Fedorov,† Victor Mougel,† Haruki Nagae,†,‡ Francisco Nuñ́ez-Zarur,† and Pavel A. Zhizhko†,§ †Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1−5, CH-8093 Zürich, Switzerland ‡Department of Chemistry, Graduate School of Engineering Science, Osaka University, CREST, Toyonaka, Osaka 560-8531, Japan A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str. 28, 119991 Moscow, Russia

Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities

Rapid development of organometallic chemistry of transition elements in recent years has greatly influenced homogeneous catalysis. Many organometallic compounds of transition metals have been directly used as effective catalysts; e.g., π-ally1 complexes of transition elements for diene reactions [1–3], carbonyl complexes for hydroformilation [4], and cyclopentadienyl and arene complexes for hydrogenation [5]. The study of stoichiometric reactions of organometallic compounds was also of great importance for homogeneous catalysis as individual organometallic compounds of various classes represent the analogs of intermediate species formed in the process of catalytic reactions (e.g., π-complexes and σ-organometallic compounds [6–8] in various reactions where the original catalyst is not an organometallic compound).

Supported Catalysts Obtained by Interaction of Organometallic Compounds of Transition Elements with Oxide Supports

Many industrial catalysts contain isolated metal sites on the surface of oxide supports. While such catalysts have been used in a broad range of processes for more than 40 years, there is often a very limited understanding about the structure of the catalytically active sites. This review discusses how Surface Organometallic Chemistry (SOMC) engineers surface sites with well-defined structures and provides insight about the nature of active sites in industrial catalysts, focusing in particular on olefin production and conversion processes

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Bridging the Gap between Industrial and Well-Defined Supported Catalysts

The Phillips supported chromium catalyst is used to produce some 40–50% of the world's high-density polyethylene. The chemistry of this important catalyst is reviewed from an industrial perspective, on the basis of more than half a century of commercial experience, as well as published research. Polymer characteristics are used as an analytical tool to probe and better understand the active-site population on the catalyst.

R.J. Wyatt

Papers

Highly active polymerization catalysts of long life derived from σ- and π-bonded transition metal alkyl compounds☆